io: preserve ipv4/ipv6 flags when resolving InetSocketAddress

The original InetSocketAddress struct may have has_ipv4 and
has_ipv6 fields set, which will control both the ai_family
used during DNS resolution, and later use of the V6ONLY
flag.

Currently the standalone DNS resolver code drops the
has_ipv4 & has_ipv6 flags after resolving, which means
the later bind() code won't correctly set V6ONLY.

This fixes the following scenarios

  -vnc :0,ipv4=off
  -vnc :0,ipv6=on
  -vnc :::0,ipv4=off
  -vnc :::0,ipv6=on

which all mistakenly accepted IPv4 clients

Acked-by: Gerd Hoffmann <kraxel@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

io/dns-resolver.c

@@ -116,8 +116,10 @@ static int qio_dns_resolver_lookup_sync_inet(QIODNSResolver *resolver,
             .numeric = true,
             .has_to = iaddr->has_to,
             .to = iaddr->to,
-            .has_ipv4 = false,
-            .has_ipv6 = false,
+            .has_ipv4 = iaddr->has_ipv4,
+            .ipv4 = iaddr->ipv4,
+            .has_ipv6 = iaddr->has_ipv6,
+            .ipv6 = iaddr->ipv6,
         };
 
         (*addrs)[i] = newaddr;